Installation guide

Wi-Fi Location-Based Services—Design and Deployment Considerations

OL-11612-01

Deployment Best Practices

As the weight assigned to the previous position is increased in relation to the weight assigned to the new

position, the more damping is applied to the movement of the device. This increased level of damping

acts to retard visible device movement. Note that the use of location damping does not imply that

changes in location are not reflected in the location display at all. Rather, the use of smoothing limits the

rate at which such changes are communicated to the end user by using smaller movement increments.

The use of location smoothing involves a small tradeoff between location viewing stability and the

reaction time of the location display to changes in position. For most environments, the use of the default

smoothing factor should provide an improved viewing experience. Higher smoothing factors are best

reserved for environments where there is very infrequent movement of WLAN clients and tagged assets.

Low smoothing factors (or no smoothing) may provide better results in situations where tagged assets

and clients are in constant or near-constant motion.

Avoiding Location Misdetection in Multi-Floor Structures

It is often necessary to perform location tracking of devices that are located on various floors in a

multi-floor vertical structure, such as a common office building. After access points have been assigned

to specific floor maps, the location appliance positioning engine considers signal strength reports only

from access points that are deemed to reside on the same floor as the mobile device. As described in this

document and other references, registered access points are assigned to floors using Monitor Maps >

Add Access Points. This section examines how the location appliance determines how to assign the

mobile device to a particular floor, and how this knowledge can be valuable to the network designer

wishing to minimize the number of floor misdetects that may occur during normal use.

Note A floor misdetect is a situation where the location appliance positioning engine indicates that the entity

in question (that is, a client, asset tag, rogue access point, or rogue client) is located on a floor that does

not match the floor on which the entity actually physically resides. When this is not because of the client

moving from one floor to another between location updates, it can be referred to as a location floor

misdetect.

When the location appliance receives signal strength information for a device from several access points

that are assigned to different floors, the positioning engine attempts to localize that device to a particular

floor via a two-step process:

1. If there are access points that detect the device with RSSI = -65 dBm, the location appliance marks

this device as being resident on the same floor as the access point with the strongest signal strength.

2. Otherwise, the location appliance considers calculating a weighted signal strength metric for each

floor, and compares the weighted metric of each floor to one another. The metric is weighted such

that it gives a numerical bias to those signal strength readings that exceed -90 dBm. The device is then

marked as resident on the floor possessing the highest weighted metric.

Because it can be expected that mobile devices may change location from floor to floor regularly, this

process repeats periodically to ensure that the mobile device is accurately assigned to the correct floor.

More smoothing (default) 75% 25%

Maximum smoothing 90% 10%

Table 2 Smoothing Factor Weight Assignments